In theory, many different wetting liquids can be used. In order to obtain a good wetting of the sample, the wetting liquid should have the following physical properties:

• Zero contact angle
• Low surface tension
• Low vapor pressure

The wetting liquids also has to be chemically inert and should not cause swelling of the sample.

In many cases, the best results are obtained by using perfluoroethers. These liquid has an extremely low surface tension (16 dynes/cm) and are almost totally immune to the problem of evaporation.

Sometimes silicone oils are used. They have a high viscosity, a low surface tension and a low vapor pressure. The only disadvantage to these silicone oils is that it is hard to clean them out of inserts or other support materials. This residual silicone oil can contaminate subsequent tests, which can prevent the Porometer from getting good dry curves.

Also water is usable, but water will only wet the hydrophilic pores and water also tends to evaporate from the pores at increased flow through the large pores of the sample. The  surface tension of water is rather high (72 dynes/cm). Also water, just as alcohol, often cause swelling of the sample.

We recommend to use as much as possible the same liquids. In theory, as long as you apply the correct vapor pressure, different liquids should give the same results. In practice, that is not always the case.

Porometer.com offers different types of wetting fluids in different quantities. All of our wetting fluids come with a certificate showing the measured surface tension.